Search engines have become popular tools to identify and locate specific information on the Internet. A search engine is a computer program that, when queried for information, retrieves either related information or pointers to the location of related information, or both, by evaluating content stored in its search database.
A key metric in evaluating the performance of search engines is relevance of the search results. Search engine developers are always striving to deliver search results that are relevant to the search query being processed. Consistent with this goal, there have been attempts to rank search results based on a number of different factors. One of the more popular ways to rank search results involves analyzing the location and frequency of keywords on a web page. Another frequently used technique is analyzing how web pages link to each other. A web page gets a ranking boost based on the number of other web pages that are linked to it. Click-through rates of search results are analyzed in some search engines. The general rule is: the higher the click-through rate, the higher the ranking.